Stability of polymer thin films on solid substrates is an integral requisite in numerous technological applications. However, this issue continues to remain a persistent challenge owing to the commonly occurring phenomenon of dewetting. Thermodynamically unfavorable polymer-substrate interactions coupled with system heterogeneities and residual stresses lead to amplification of destabilizing surface capillary waves, causing a spontaneous rupture of the film and rendering it unusable for most applications. The objective of this research was twofold: to develop interfacial strategies for suppression of polymer thin film dewetting, by addressing the film destabilizing factors of unfavorable polymer-substrate interactions and capillary waves enhancement at the polymer–air interface. Model dewetting homopolymer systems of low molecular weight polystyrene (PS) and polybutadiene (PB) and their symmetric blends were used in this study.
Firstly, the tunability of polymer-substrate interactions via addition of fullerene (C60) nanoparticles (NP) to symmetric PS/PB blend thin films was investigated. Three distinct regimes of film stability and morphology as a function of NP concentration were observed via optical, confocal and atomic force microscopy, and analyzed using particle and FFT analysis. In the low NP concentration range of 1-7 mass %, preferential segregation of the NPs to the polymeric interface in the blend led to macroscopic dewetting. In the intermediate range of 7-11 mass%, the NPs enriched the polymer-substrate interface sufficiently to inhibit film dewetting and formed a percolating blend-NP structure. At filler concentrations above 11 mass %, spinodal clustering of the -NPs gave rise to polymer-NP phase exclusion and subsequent dewetting that evolved from concentration waves around the NPs.
Secondly, a novel method to suppress film surface capillary waves was developed. It was discovered that confinement of a PS thin film by an imprinted elastomer sheet with features less than the natural capillary wavelength could suppress dewetting. The elastic confinement was shown to retard the dewetting dynamics by interrupting the correlated amplification of capillary waves aided by the high energy penalty of deformation. Elastomer sheets with or without patterns comparable to capillary wavelength did not suppress dewetting. Pattern amplitude above a critical value and lateral pitch below the capillary wavelength completely suppressed dewetting.
|Advisor:||Karim, Alamgir, Becker, Matthew L.|
|Commitee:||Becker, Matthew L., Jana, Sadhan, Karim, Alamgir, Shawkey, Matthew, Weiss, Robert|
|School:||The University of Akron|
|School Location:||United States -- Ohio|
|Source:||DAI-B 78/11(E), Dissertation Abstracts International|
|Keywords:||Capillary waves, Controlling polymer thin film instabilities, Suppression, Tuning of polymer-substrate interactions|
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